US20130149118A1 - Labyrinth seals - Google Patents
Labyrinth seals Download PDFInfo
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- US20130149118A1 US20130149118A1 US13/538,402 US201213538402A US2013149118A1 US 20130149118 A1 US20130149118 A1 US 20130149118A1 US 201213538402 A US201213538402 A US 201213538402A US 2013149118 A1 US2013149118 A1 US 2013149118A1
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- fin
- fins
- upstream
- labyrinth seal
- sealing
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
- F01D—NON-POSITIVE DISPLACEMENT MACHINES OR ENGINES, e.g. STEAM TURBINES
- F01D11/00—Preventing or minimising internal leakage of working-fluid, e.g. between stages
- F01D11/02—Preventing or minimising internal leakage of working-fluid, e.g. between stages by non-contact sealings, e.g. of labyrinth type
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
- F01D—NON-POSITIVE DISPLACEMENT MACHINES OR ENGINES, e.g. STEAM TURBINES
- F01D11/00—Preventing or minimising internal leakage of working-fluid, e.g. between stages
- F01D11/08—Preventing or minimising internal leakage of working-fluid, e.g. between stages for sealing space between rotor blade tips and stator
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
- F01D—NON-POSITIVE DISPLACEMENT MACHINES OR ENGINES, e.g. STEAM TURBINES
- F01D5/00—Blades; Blade-carrying members; Heating, heat-insulating, cooling or antivibration means on the blades or the members
- F01D5/12—Blades
- F01D5/22—Blade-to-blade connections, e.g. for damping vibrations
- F01D5/225—Blade-to-blade connections, e.g. for damping vibrations by shrouding
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
- F16J—PISTONS; CYLINDERS; SEALINGS
- F16J15/00—Sealings
- F16J15/44—Free-space packings
- F16J15/447—Labyrinth packings
- F16J15/4472—Labyrinth packings with axial path
Definitions
- the present invention relates generally to labyrinth seals, and particularly to labyrinth seals for sealing between static and moving parts in turbomachines, such as axial flow gas turbines, steam turbines, or compressors.
- Labyrinth seals are commonly used to provide a seal, and therefore minimize fluid leakage, between static and rotating parts in turbomachines, such as axial flow gas turbines or steam turbines.
- FIG. 1 of EP 1001139 A1 A conventional labyrinth seal for sealing between the tips of moving blades and the radially adjacent static casing in an axial flow turbine is illustrated in FIG. 1 of EP 1001139 A1.
- this conventional labyrinth seal axially spaced and circumferentially extending sealing fins are caulked into the static casing and project radially inwardly, across the fluid flow path, towards castellated arcuate blade shrouds at the blade tips.
- a radial clearance is normally provided between the tip of each sealing fin and the radially adjacent arcuate blade shrouds to prevent or minimize rubbing contact between the tips of the static sealing fins and the moving blade shrouds during radial excursions of the moving blade shrouds relative to the radially adjacent static casing.
- the present disclosure is directed to a labyrinth seal arranged to impede leakage flow though a gap between confronting surfaces of static and moving parts in an axial fluid flow turbomachine.
- the labyrinth seal includes a plurality of axially spaced and circumferentially extending sealing fins arranged in leakage flow series, the fins projecting across the gap from at least one of the confronting parts towards an opposing confronting part such that distal ends of the fins are in sealing proximity to the opposing confronting part.
- the labyrinth seal also includes a plurality of chambers defined by successive fins in leakage flow series.
- Each fin has an upstream-facing surface of which at least a distal portion thereof is inclined towards the upstream direction of the leakage flow to form a vortex-producing flow recirculation surface operative to deflect the leakage flow in the upstream direction and create recirculating vortices in the leakage flow within the chambers defined by successive fins.
- FIG. 2 is an enlarged view of a fin forming part of FIG. 1 ;
- FIGS. 3 and 4 are views similar to FIG. 2 , but showing two possible variants of the shape of the fin of FIG. 2 ;
- FIG. 5 is a view similar to FIG. 1 , but showing a second major embodiment of a labyrinth seal
- FIG. 6 is an enlarged view of a fin forming part of FIG. 5 ;
- FIGS. 7 and 8 are views similar to FIG. 6 , but showing two possible variants of the shape of the fin of FIG. 6 .
- the present disclosure provides a labyrinth seal arranged to impede leakage flow though an annular gap between confronting surfaces of static and moving parts in an axial fluid flow turbomachine, the labyrinth seal comprising:
- distal end means the end of the fin that is most distant from the surface from which the fin projects and the term “distal portion” means a part of the fin, including the fin's distal end, that is most distant from the surface from which the fin projects.
- distal portion means a part of the fin, including the fin's distal end, that is most distant from the surface from which the fin projects.
- the flow recirculation surfaces of the circumferentially extending sealing fins divert and recirculate fluid that is flowing downstream along the fluid leakage path, back in an upstream direction. This reduces leakage flow through the radial clearances between the distal ends of the sealing fins and the surface of the radially adjacent static or moving part of the turbomachine and results in a reduced effective leakage area and hence a reduced discharge coefficient.
- a fluid recirculation zone is created between axially adjacent sealing fins and the flow recirculation surface of the downstream sealing fin generates a vortex flow within the fluid recirculation zone.
- the generated vortex flow increases the pressure drop across the sealing fins and thereby reduces leakage through the radial clearances between the tips of the sealing fins and the surface of the radially adjacent static or moving part of the turbomachine.
- the reduced leakage flow increases the sealing effectiveness of the labyrinth seal.
- one of the confronting surfaces of the static and moving parts is castellated and comprises at least one land and at least one relatively recessed portion, each land and each recessed portion being in sealing proximity to the distal end of a sealing fin and wherein successive sealing fins alternately comprise a first fin having a straight upstream-facing surface inclined towards the upstream direction and a second fin having an upstream-facing surface of which at least the distal portion is inclined towards the upstream direction.
- first fin and “second fin” used herein are intended to identify the sealing fins, not to restrict whether they are arranged first or second in fluid flow sequence.
- the upstream-facing surface of the/each first sealing fin may be inclined in the upstream direction at an acute angle of between 10 and 70 degrees, preferably 45 degrees, away from the radial direction.
- each first fin is in sealing proximity to a land and the distal end of each second fin is in sealing proximity to a recessed portion.
- Alternate lands and recessed portions are provided in one of the confronting surfaces so that the leakage flow has a less direct route through the labyrinth seal than would be the case if the surface were merely planar, thereby increasing the resistance of the labyrinth seal to the leakage flow. Additionally, the recessed portions provide the recirculating vortices with a greater radial height and chamber volume in which to fully develop, thereby provide maximum recirculation of any leakage flow and further increasing the flow resistance of the labyrinth seal.
- the flow recirculation surface formed by the inclined distal portion of the/each second fin may be a concavely curved portion of the second fin's upstream-facing surface.
- the most upstream fin is a first fin whose distal end is in sealing proximity to a land, and the immediately succeeding fin is a second fin whose distal end is in sealing proximity to a recessed surface portion.
- the most upstream fin is a second fin whose distal end is in sealing proximity to a recessed surface portion and the immediately succeeding fin is a first fin whose distal end is in sealing proximity to a land.
- the or each of the first sealing fins may project from the static or moving part across the fluid flow path into a corresponding recessed portion of a confronting moving or static surface, and the or each of the second circumferentially extending sealing fins may project from the static or moving part across the fluid flow path towards a corresponding land.
- each second fin preferably comprises a radially extending portion projecting from the static or moving part and an inclined distal portion adjacent the fin's distal end.
- the distal portion of the upstream-facing surface of each second fin may be inclined over a distance in the range of about 20% to about 50%, preferably about 30%, of the length of the fin.
- the upstream-facing surface of the or each second fin is concavely curved over its whole length, maximum concavity being at its distal end.
- first and second sealing fins are provided on the static part and the castellated surface is provided on the moving part.
- first and second sealing fins may be provided on the moving part and the castellated surface may be provided on the static part, so that the first and second sealing fins project across the fluid flow path from the moving part towards the castellated surface on the static part.
- successive sealing fins alternately comprise a static fin projecting from the static part into sealing proximity with the moving part and a moving fin projecting from the moving part into sealing proximity with the static part.
- the most upstream fin in the labyrinth seal is a static fin.
- the most upstream fin in the labyrinth seal may be a moving fin.
- the upstream-facing surfaces of the static and moving sealing fins comprise radially extending portions projecting from the static and moving parts, respectively, and inclined distal portions adjacent the distal ends of the fins.
- the distal portions of the upstream-facing surfaces of the fins may be inclined over a distance in the range of about 20% to about 50%, preferably 30%, of the lengths of the fins.
- the inclined distal portions of the static and moving sealing fins comprise concavely curved portions of the upstream-facing surfaces, but alternatively the upstream-facing surfaces of the sealing fins may be concavely curved over their whole lengths, maximum concavity being at their distal ends.
- abradable material may be provided on the surfaces of the moving and/or static parts, as appropriate, adjacent the distal ends of the sealing fins.
- abradable material may be provided on the surfaces of the moving and/or static parts, as appropriate, adjacent the distal ends of the sealing fins.
- the distal ends of the sealing fins will rub against the abradable material rather than the solid metal of the static or moving part. Since it is arranged that the abradable material is softer or at least wears away more easily than the material at the distal ends of the sealing fins, the shape and sealing effectiveness of the fins is preserved.
- a further aspect of the invention provides a turbomachine, comprising a static part, a moving part and a labyrinth seal according to the first or second major embodiments for sealing between the static and moving parts.
- the turbomachine may be an axial flow turbine, such as a steam turbine or a gas turbine.
- the moving part may be a moving arcuate blade shroud mounted on the radially outer tip of a moving turbine blade.
- the static part may be a static casing positioned radially outwardly of the moving blade shroud.
- the moving part may be a rotor shaft and the static part may be a static diaphragm ring positioned radially outwardly of the rotor shaft.
- the labyrinth seal may thus be arranged to seal between an inner diameter of the static diaphragm ring and the radially inner rotor.
- An axial flow turbine such as a gas turbine or steam turbine, generally includes a plurality of turbine stages, each stage comprising an annular array of angularly spaced-apart moving blades, preceded by an annular array of angularly spaced-apart static vanes whose function is to guide the turbine working fluid onto the moving blades.
- FIG. 1 there is shown the radially outer part of a moving blade comprising an aerofoil portion 10 and an arcuate blade shroud 11 , which is mounted on and integral with the radially outer tip of the aerofoil portion 10 .
- Adjacent blade shrouds 11 cooperate to form an annular shroud ring.
- a circumferentially extending static casing 12 is positioned radially outwardly of, and surrounds, the moving blades.
- each blade shroud 11 has a radially outer castellated surface 14 formed by a plurality of axially spaced-apart, radially outer, circumferentially extending lands 16 , each land 16 being followed by a relatively recessed, radially inner surface portion 18 that is circumferentially co-extensive with the land.
- FIG. 1 shows a shroud surface with two lands 16 , it is at the option of the skilled person to incorporate as many lands as may be convenient and useful in the particular circumstances of the turbine design being considered. Normally, however, there will be a plurality of lands 16 in order to decrease leakage of working fluid through the gap between the shroud 11 and the static casing 12 , as hereafter explained.
- Working fluid is expanded through the axial flow turbine and moves along a fluid flow path between the moving blade aerofoils 10 in a downstream direction, as shown by arrow 19 in FIG. 1 .
- a labyrinth seal 20 seals between the moving blade shrouds 11 and the radially adjacent static casing 12 to minimize fluid leakage 21 past the blade shrouds 11 at the tips of the moving blades.
- the labyrinth seal 20 includes a plurality of first circumferentially extending and axially spaced sealing fins 24 which project radially inwardly from the static casing 12 across the leakage fluid flow path towards the lands 16 on the castellated surface 14 of the moving blade shrouds 11 .
- the labyrinth seal 20 also includes a plurality of second circumferentially extending and axially spaced sealing fins 26 which likewise project radially inwardly from the static casing 12 across the leakage fluid flow path towards the relatively recessed radially inner portions 18 of the castellated surface 14 of the moving blade shrouds 11 .
- the first and second circumferentially extending sealing fins 24 , 26 are alternately arranged along the static casing 12 in the axial direction, such that each of the first sealing fins 24 is followed by a second sealing fin 26 .
- the first and second circumferentially extending sealing fins 24 , 26 may be manufactured as separate components and secured, e.g., by a caulking process, as known per se, in circumferentially extending recesses (not shown) in the static casing 12 .
- the correct radial clearances to use can be calculated by computer modeling of the operating behavior of the turbine or determined by rig tests.
- the radial clearances chosen are generally sufficient to prevent rubbing contact between the tips of the first and second sealing fins 24 , 26 and the castellated surface 14 of the adjacent moving blade shrouds 11 during most radial excursions of the moving blade shrouds 11 relative to the static casing 12
- larger radial excursions which may be outside normal turbine operating behavior, can be tolerated by providing abradable material 27 on the castellated surface 14 of the blade shrouds 11 adjacent the tips of the first and second sealing fins 24 , 26 .
- the abradable material 27 which is softer than the material at the tips of the sealing fins 24 , 26 , is worn away by the tips of the sealing fins 24 , 26 during radial excursions of the moving blade shrouds 11 . Damage to the tips of the sealing fins 24 , 26 is, thus, prevented or at least minimized, thereby preserving the shape of the tips of the first and second sealing fins 24 , 26 and hence the sealing effectiveness of the sealing fins 24 , 26 .
- Abradable materials suitable for the above purpose are, for example, thermal-sprayed coatings of various types, such as cermets.
- a well-known alternative is Feltmetal®, comprising metal fiber felts made from a variety of high temperature resistant alloys, the fibers in the felts being randomly interlocked by a sintering process.
- Feltmetal® is manufactured by Technetics, 1700 E. Int'l Speedway Blvd., DeLand, Fla. 32724 USA.
- Each of the first sealing fins 24 is inclined in an upstream direction and defines an acute angle ‘A’ relative to the radial direction. In the present case angle A is about 45 degrees away from the radial direction, but in other embodiments angle A may vary between about 10 and 70 degrees. Accordingly, each of the first sealing fins 24 has a linear (i.e. non-curved) upstream-facing surface 28 which is oriented at the acute angle A, in the aforesaid range.
- Each of the first sealing fins 24 is mounted on the static casing 12 and projects across the leakage flow path so that its distal end is in sealing proximity with a corresponding circumferential land 16 of the castellated surface 14 of the moving blade shrouds 11 .
- each of the first sealing fins 24 cooperates with the corresponding circumferentially extending land 16 and forms a vortex-producing flow recirculation surface operative to deflect leakage flow 21 back in an upstream direction, thereby creating recirculating vortices 25 in the leakage flow. Leakage flow 21 past the tips of the first sealing fins 24 is thus reduced.
- each of the second sealing fins 26 includes an upstream-facing surface 30 , comprising a first fin portion 32 which projects in a substantially radially inward direction from the static casing 12 across the leakage flow path, and a second, distal portion 34 adjacent to and including the fin's tip, this distal portion being inclined towards the upstream direction, i.e., towards the downstream surface of an immediately upstream sealing fin, where such a fin is present.
- the inclined distal portion 34 of each second fin 26 is a concavely curved portion of the upstream-facing surface 30 .
- This concavely curved portion forms a vortex-producing flow recirculation surface, which extends over a distance comprising about 30% of the total length L of the fin 26 measured between its tip and the surface from which it projects.
- the curvature may extend over a distance in the range of about 20% to about 50% of the fin's length between its tip and the static casing surface 12 from which it projects.
- concavely curved distal portion 34 of upstream-facing surface 30 of fins 26 is shown as an arc of a circle, the skilled person will realize that the curve could alternatively be an arc of an ellipse or other conic section.
- the concavely curved distal portion 34 of upstream-facing surface 30 of fins 26 may be approximated by a straight (linear) distal portion, inclined at an angle relative to the radial direction. This is illustrated in FIG. 3 , where a fin 26 A of length L has an upstream-facing surface 30 A with a straight distal portion 34 A that is inclined at an angle ‘B’ to the radial direction to form a vortex-producing flow recirculation surface. Similarly to the curved distal portion 34 in FIG. 2 , distal portion 34 A in FIG.
- the inclined portion 3 is inclined over a distance comprising about 30% of the total length L of the fin 26 measured between its tip and the surface from which it projects, but in other embodiments the inclined portion may extend over a distance comprising between about 20% and about 50% of the fin's length between its tip and the surface from which it projects.
- angle B in FIG. 3 may be in the range of about 10 degrees to about 60 degrees, preferably about 25 degrees to about 45 degrees, and if the length L of the fin is 10 mm, the inclined distal portion 34 A of the upstream-facing surface 30 A may occupy about the last 3 to 4 mm of the fin adjacent the tip, measured in the radial direction
- FIG. 4 illustrates a further alternative embodiment, which may be preferred from the aspect of enabling greater sealing efficiency.
- the whole of the upstream-facing surface 30 B of the fin 26 B is curved in the upstream direction, not merely the distal portion.
- the angle that the upstream-facing surface 30 B makes to the radial direction gradually increases from zero at a point where the fin projects from the static or moving surface, to a maximum angle B at the tip 340 B of the fin.
- the surface 300 B could be elliptically, parabolically or hyperbolically curved.
- angle B may be in the range of about 10 degrees to about 60 degrees, preferably about 25 degrees to about 45 degrees.
- the shapes of the fins 26 , 28 deflect leakage fluid 21 back in an upstream direction, thus creating recirculating vortex flows 25 , 36 in the axially and circumferentially extending chambers 40 , 42 defined between successive fins. .
- the vortices make it difficult for the leakage flow to exit through the gaps between the tips of the fins and the adjacent moving surfaces, resulting in a reduced effective area and therefore a smaller coefficient of fluid discharge through the gaps.
- the generated vortices contribute to a larger pressure drop across the fins and therefore reduced leakage. Leakage flow past the tips of the fins is thus reduced.
- first and second circumferentially extending sealing fins 24 , 26 increases, the disruption and recirculation of the leakage fluid flowing along the fluid flow path also increases.
- the disruption of the leakage flow that is provided by the arrangement of the first and second circumferentially extending sealing fins 24 , 26 of the labyrinth seal illustrated in FIG. 2 has been found to provide a reduction in leakage flow between the castellated surface 14 of the moving blade shrouds 11 and the static casing 12 of about 19% compared to conventional labyrinth seal designs such as that shown in FIG. 1 of EP 1001139 A1.
- the efficiency of an axial flow turbine including the labyrinth seal is thus appreciably improved.
- the shroud surface 14 is provided with alternate lands 16 and recessed portions 18 so that the leakage flow 21 has a less direct route through the labyrinth seal than would be the case if the shroud surface were merely planar. This increases the resistance of the labyrinth seal to the leakage flow.
- the recessed portions 18 provide vortices 36 with a greater radial height and chamber volume in which to fully develop, thereby further increasing resistance of the labyrinth seal to the leakage flow.
- first and/or second circumferentially extending sealing fins 24 , 26 could be mounted on the moving blade shrouds 11 for rotation therewith.
- the radially inner surface of the static casing 12 would be castellated so that the first and second circumferentially extending sealing fins 24 , 26 project radially outwardly from the blade shrouds 11 , across the fluid flow path, towards the castellated surface 14 of the static casing 12 .
- FIG. 1 shows four sealing fins arranged in flow series, i.e., two first fins 24 , each of which is followed by a second fin 26 , it should be realized that if desired, this sequence could be extended indefinitely, e.g., six sealing fins comprising three first fins 24 , each of which is followed by a second fin 26 . Conversely, in some situations, it may be possible to achieve acceptable sealing performance using two first fins 24 , with one second fin 26 located between the two fins 24 , or even only one first fin 24 followed by only one second fin 26 .
- FIG. 1 illustrates a presently preferred arrangement, in which the most upstream fin is a first fin 24 whose distal end is in sealing proximity to a land 16 , and the immediately succeeding fin is a second fin 26 whose distal end is in sealing proximity to a recessed surface portion 18 , it may also be possible to obtain a desirable increase in efficiency if the order of the first and second fins is reversed, so that the most upstream fin is a second fin 26 whose distal end is in sealing proximity to a recessed surface portion 18 and the immediately succeeding fin is a first fin 24 whose distal end is in sealing proximity to a land 16 .
- FIGS. 5 to 8 A second major embodiment will now be described with reference to FIGS. 5 to 8 .
- Working fluid is expanded through the axial flow turbine and moves along a fluid flow path between the moving blade airfoils 100 in a downstream direction, as shown by arrow 190 in FIG. 1 .
- a labyrinth seal 200 seals between the moving blade shrouds 110 and the radially adjacent static casing 120 to minimize fluid leakage 210 past the blade shrouds 110 at the tips of the moving blades.
- first sealing fins 240 projecting inwardly from the static casing 120
- second sealing fins 260 projecting outwardly from the moving blade shrouds 110
- the static and moving sealing fins 240 , 260 are alternately arranged in the axial direction through the labyrinth seal 200 , such that each static sealing fin 240 is followed by a moving sealing fin 260 .
- the static sealing fins 240 project into axial spaces between the moving sealing fins 260
- the moving sealing fins 260 project into axial spaces between the static sealing fins.
- the static and moving sealing fins 240 , 260 may be manufactured as separate components and secured, e.g., by a caulking process, as known per se, in circumferentially extending recesses (not shown) in the static casing 120 and the moving blade shrouds 110 , respectively.
- the radial clearances chosen are generally sufficient to prevent rubbing contact between the tips of the static and moving sealing fins 240 , 260 and the adjacent moving blade shrouds 110 or static casing 120 during most radial excursions of the moving blade shrouds 110 relative to the static casing 120 , larger radial excursions, which may be outside normal turbine operating behavior, can be tolerated by providing abradable material 270 on or in the surfaces 140 , 122 of the moving blade shrouds 110 and the static casing 120 adjacent the tips of the static sealing fins 240 and the moving sealing fins 260 .
- the abradable material 270 which is softer than the material at the tips of the sealing fins 240 , 260 , is worn away by the tips of the sealing fins during radial excursions of the moving blade shrouds 110 . Deformation to the tips of the sealing fins 240 , 260 is, thus, prevented or at least minimized, thereby preserving the effectiveness of the labyrinth seal 200 .
- Abradable materials suitable for the above purpose are, for example, thermal-sprayed coatings of various types, such as cermets.
- a well-known alternative is Feltmetal®, comprising metal fibre felts made from a variety of high temperature resistant alloys, the fibres in the felts being randomly interlocked by a sintering process.
- Feltmetal® is manufactured by Technetics, 1700 E. Int'l Speedway Blvd., DeLand, Fla. 32724 USA.
- each of the static and moving sealing fins 240 , 260 includes a vortex-producing flow recirculation surface which faces in the upstream direction relative to the flow of leakage air through the labyrinth seal 200 .
- each sealing fin 240 , 260 has an upstream-facing surface 300 that includes a straight fin portion 320 projecting in a substantially radial direction from either the static casing 120 or the moving blade shroud 110 across the leakage flow path, and a distal portion 340 near its distal end, which is inclined towards the upstream direction of the leakage flow.
- the inclined distal portion 340 is a concavely curved portion of the fin's upstream-facing surface 240 , and comprises a vortex-producing flow recirculation surface, which extends over a distance comprising about 30% of the total length L of the fins measured between their tips and the surface from which they project.
- the concave curvature may extend over a distance in the range of about 20% to about 50% of the fin's length between its tip and the static or moving surface from which it projects.
- the concavely curved distal portion 340 of upstream-facing surface 300 of fins 240 , 260 is shown as an arc of a circle with radius R, the skilled person will realize that the curve could alternatively be an arc of an ellipse or other conic section.
- the concavely curved distal portion 340 of upstream-facing surface 300 may be approximated by a straight distal portion, inclined at an angle relative to the radial direction. This is illustrated in FIG. 7 , where a fin 260 A of length L has an upstream-facing surface 300 A that includes a straight fin portion 320 A projecting in a substantially radial direction from either the static casing 120 or the moving blade shroud 110 across the leakage flow path, and a straight distal portion 340 A that is inclined at an angle ‘B’ to the radial direction to form a vortex-producing flow recirculation surface.
- the inclined portion is inclined over a distance comprising about 30% of the total length L of the fin measured between its tip and the surface from which it projects, but in other embodiments the inclined portion may extend over a distance comprising between about 20% and about 50% of the fin's length between its tip and the surface from which it projects.
- angle B in FIG. 7 may be in the range of about 10 degrees to about 60 degrees, preferably about 25 degrees to about 45 degrees, and if the length L of the fin is 10 mm, the inclined distal portion 340 A of the upstream-facing surface 300 A may occupy about the last 3 to 4 mm of the fin adjacent the tip, measured in the radial direction.
- FIG. 8 illustrates a further alternative embodiment, which may be preferred from the aspect of enabling greater sealing efficiency.
- the whole of the upstream-facing surface 300 B of the fin is concavely curved, not merely the distal portion.
- the angle that the upstream-facing surface 300 B makes to the radial direction gradually increases from zero at a point 320 B where the fin projects from the static or moving surface, to a maximum angle B at the tip 340 B of the fin.
- the surface 300 B could be elliptically, parabolically or hyperbolically curved.
- angle B may be in the range of about 10 degrees to about 60 degrees, preferably about 25 degrees to about 45 degrees.
- the complementary shapes of the vortex-producing flow recirculation surfaces 340 of the static and moving fins 240 , 260 are effective to produce recirculating vortices 360 in the axially and circumferentially extending chambers 400 defined between successive static and moving fins 240 , 260 .
- the vortices make it difficult for the leakage flow to exit through the gaps between the tips of the fins and the adjacent static or moving surfaces, resulting in a reduced effective area and therefore a smaller coefficient of fluid discharge through the gaps.
- the generated vortices contribute to a larger pressure drop across the fins and therefore reduced leakage.
- an additional vortex 370 will be generated in the leakage flow before it enters the labyrinth by the flow recirculation surface of the most upstream fin 240 , though this vortex may be weaker than the vortices produced in chambers 400 .
- all the vortices 360 , 370 are shown as rotating in the same direction, it is possible that vortices in adjacent chambers 400 may rotate in opposed directions, thereby further increasing the resistance of the labyrinth seal 200 to leakage flow.
- labyrinth seal illustrated in FIG. 5 includes a plurality of static sealing fins 240 and a plurality of moving sealing fins 260 , it is possible that a labyrinth seal of this type could comprise only a single pair of fins, comprising a static sealing fin and a moving sealing fin.
- FIG. 5 illustrates a presently preferred arrangement, in which each of the static fins 240 precedes in flow sequence a moving fin 260 , it may also be possible to obtain a desirable increase in efficiency if the order of the static and moving fins is reversed, so that moving fins precede static fins.
- this would give an arrangement in which the first, third and fifth fins in streamwise sequence would be moving fins 240 and the second and fourth fins would be static fins 240 .
- the moving part could be a turbine rotor shaft and the static part could be a static turbine diaphragm ring penetrated by the shaft.
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Abstract
Description
- The present application hereby claims priority under 35 U.S.C. Section 119 to Great Britain Patent application number 1111287.7, filed Jul. 4, 2011, the entire contents of which are hereby incorporated by reference.
- The present invention relates generally to labyrinth seals, and particularly to labyrinth seals for sealing between static and moving parts in turbomachines, such as axial flow gas turbines, steam turbines, or compressors.
- Labyrinth seals are commonly used to provide a seal, and therefore minimize fluid leakage, between static and rotating parts in turbomachines, such as axial flow gas turbines or steam turbines.
- A conventional labyrinth seal for sealing between the tips of moving blades and the radially adjacent static casing in an axial flow turbine is illustrated in
FIG. 1 of EP 1001139 A1. In this conventional labyrinth seal, axially spaced and circumferentially extending sealing fins are caulked into the static casing and project radially inwardly, across the fluid flow path, towards castellated arcuate blade shrouds at the blade tips. A radial clearance is normally provided between the tip of each sealing fin and the radially adjacent arcuate blade shrouds to prevent or minimize rubbing contact between the tips of the static sealing fins and the moving blade shrouds during radial excursions of the moving blade shrouds relative to the radially adjacent static casing. - In conventional labyrinth seals such as that shown in
FIG. 1 of EP 1001139 A1, axially flowing working fluid can escape through the radial clearances provided between the tips of the sealing fins and the radially adjacent arcuate blade shrouds, thus reducing the effectiveness of the labyrinth seal. - It is, therefore, desirable to provide labyrinth seals with improved sealing capability.
- The present disclosure is directed to a labyrinth seal arranged to impede leakage flow though a gap between confronting surfaces of static and moving parts in an axial fluid flow turbomachine. The labyrinth seal includes a plurality of axially spaced and circumferentially extending sealing fins arranged in leakage flow series, the fins projecting across the gap from at least one of the confronting parts towards an opposing confronting part such that distal ends of the fins are in sealing proximity to the opposing confronting part. The labyrinth seal also includes a plurality of chambers defined by successive fins in leakage flow series. Each fin has an upstream-facing surface of which at least a distal portion thereof is inclined towards the upstream direction of the leakage flow to form a vortex-producing flow recirculation surface operative to deflect the leakage flow in the upstream direction and create recirculating vortices in the leakage flow within the chambers defined by successive fins.
- Embodiments of the present invention will now be described by way of example only and with reference to the accompanying drawings, in which:
-
FIG. 1 is a diagrammatic cross-sectional view of a first major embodiment of a labyrinth seal viewed in the circumferential direction of an axial flow turbine in which it is installed; -
FIG. 2 is an enlarged view of a fin forming part ofFIG. 1 ; -
FIGS. 3 and 4 are views similar toFIG. 2 , but showing two possible variants of the shape of the fin ofFIG. 2 ; -
FIG. 5 is a view similar toFIG. 1 , but showing a second major embodiment of a labyrinth seal; -
FIG. 6 is an enlarged view of a fin forming part ofFIG. 5 ; and -
FIGS. 7 and 8 are views similar toFIG. 6 , but showing two possible variants of the shape of the fin ofFIG. 6 . - The present disclosure provides a labyrinth seal arranged to impede leakage flow though an annular gap between confronting surfaces of static and moving parts in an axial fluid flow turbomachine, the labyrinth seal comprising:
-
- a plurality of axially spaced and circumferentially extending sealing fins arranged in leakage flow series, the fins projecting across the gap from at least one of the confronting parts towards an opposing confronting part such that distal ends of the fins are in sealing proximity to the opposing confronting part;
- a plurality of chambers defined between successive fins in leakage flow series;
- each fin having an upstream-facing surface of which at least a distal portion thereof is inclined towards the upstream direction of the leakage flow to form a vortex-producing flow recirculation surface operative to deflect the leakage flow in the upstream direction and create recirculating vortices in the leakage flow within the chambers defined by successive fins.
- As used herein, the term “distal end” means the end of the fin that is most distant from the surface from which the fin projects and the term “distal portion” means a part of the fin, including the fin's distal end, that is most distant from the surface from which the fin projects. Use of the term “sealing proximity” means that there is a small radial clearance between the distal end of a sealing fin and the surface against which it seals, such clearance being insufficient to seriously compromise the sealing efficiency of the labyrinth seal.
- The flow recirculation surfaces of the circumferentially extending sealing fins divert and recirculate fluid that is flowing downstream along the fluid leakage path, back in an upstream direction. This reduces leakage flow through the radial clearances between the distal ends of the sealing fins and the surface of the radially adjacent static or moving part of the turbomachine and results in a reduced effective leakage area and hence a reduced discharge coefficient. A fluid recirculation zone is created between axially adjacent sealing fins and the flow recirculation surface of the downstream sealing fin generates a vortex flow within the fluid recirculation zone. The generated vortex flow increases the pressure drop across the sealing fins and thereby reduces leakage through the radial clearances between the tips of the sealing fins and the surface of the radially adjacent static or moving part of the turbomachine. The reduced leakage flow increases the sealing effectiveness of the labyrinth seal.
- In one major embodiment disclosed herein, one of the confronting surfaces of the static and moving parts is castellated and comprises at least one land and at least one relatively recessed portion, each land and each recessed portion being in sealing proximity to the distal end of a sealing fin and wherein successive sealing fins alternately comprise a first fin having a straight upstream-facing surface inclined towards the upstream direction and a second fin having an upstream-facing surface of which at least the distal portion is inclined towards the upstream direction.
- Note that the terms “first fin” and “second fin” used herein are intended to identify the sealing fins, not to restrict whether they are arranged first or second in fluid flow sequence.
- To obtain disruption and recirculation of the leakage flow, the upstream-facing surface of the/each first sealing fin may be inclined in the upstream direction at an acute angle of between 10 and 70 degrees, preferably 45 degrees, away from the radial direction.
- Preferably, the distal end of each first fin is in sealing proximity to a land and the distal end of each second fin is in sealing proximity to a recessed portion.
- Alternate lands and recessed portions are provided in one of the confronting surfaces so that the leakage flow has a less direct route through the labyrinth seal than would be the case if the surface were merely planar, thereby increasing the resistance of the labyrinth seal to the leakage flow. Additionally, the recessed portions provide the recirculating vortices with a greater radial height and chamber volume in which to fully develop, thereby provide maximum recirculation of any leakage flow and further increasing the flow resistance of the labyrinth seal.
- The flow recirculation surface formed by the inclined distal portion of the/each second fin may be a concavely curved portion of the second fin's upstream-facing surface.
- In one preferred variant of the labyrinth seal, the most upstream fin is a first fin whose distal end is in sealing proximity to a land, and the immediately succeeding fin is a second fin whose distal end is in sealing proximity to a recessed surface portion. In an alternative arrangement, the most upstream fin is a second fin whose distal end is in sealing proximity to a recessed surface portion and the immediately succeeding fin is a first fin whose distal end is in sealing proximity to a land.
- In further alternative embodiments, the or each of the first sealing fins may project from the static or moving part across the fluid flow path into a corresponding recessed portion of a confronting moving or static surface, and the or each of the second circumferentially extending sealing fins may project from the static or moving part across the fluid flow path towards a corresponding land.
- For ease of manufacture, the upstream-facing surface of each second fin preferably comprises a radially extending portion projecting from the static or moving part and an inclined distal portion adjacent the fin's distal end. The distal portion of the upstream-facing surface of each second fin may be inclined over a distance in the range of about 20% to about 50%, preferably about 30%, of the length of the fin.
- In an alternative configuration, which may yield superior sealing performance, but which may be more difficult or expensive to manufacture, the upstream-facing surface of the or each second fin is concavely curved over its whole length, maximum concavity being at its distal end.
- In a preferred arrangement, the first and second sealing fins are provided on the static part and the castellated surface is provided on the moving part. Alternatively, the first and second sealing fins may be provided on the moving part and the castellated surface may be provided on the static part, so that the first and second sealing fins project across the fluid flow path from the moving part towards the castellated surface on the static part.
- In a second major embodiment, successive sealing fins alternately comprise a static fin projecting from the static part into sealing proximity with the moving part and a moving fin projecting from the moving part into sealing proximity with the static part. Preferably, the most upstream fin in the labyrinth seal is a static fin. Alternatively, the most upstream fin in the labyrinth seal may be a moving fin.
- In one variant, the upstream-facing surfaces of the static and moving sealing fins comprise radially extending portions projecting from the static and moving parts, respectively, and inclined distal portions adjacent the distal ends of the fins. For example, the distal portions of the upstream-facing surfaces of the fins may be inclined over a distance in the range of about 20% to about 50%, preferably 30%, of the lengths of the fins.
- Preferably, the inclined distal portions of the static and moving sealing fins comprise concavely curved portions of the upstream-facing surfaces, but alternatively the upstream-facing surfaces of the sealing fins may be concavely curved over their whole lengths, maximum concavity being at their distal ends.
- To prevent or ameliorate damage to the distal ends of the sealing fins in both the above major embodiments, due to excessive radial excursions of the moving shroud ring relative to the static casing, abradable material may be provided on the surfaces of the moving and/or static parts, as appropriate, adjacent the distal ends of the sealing fins. In the event of excessive radial excursions of the moving part relative to the static part during operation of the axial flow turbomachine, the distal ends of the sealing fins will rub against the abradable material rather than the solid metal of the static or moving part. Since it is arranged that the abradable material is softer or at least wears away more easily than the material at the distal ends of the sealing fins, the shape and sealing effectiveness of the fins is preserved.
- A further aspect of the invention provides a turbomachine, comprising a static part, a moving part and a labyrinth seal according to the first or second major embodiments for sealing between the static and moving parts.
- The turbomachine may be an axial flow turbine, such as a steam turbine or a gas turbine. In particular, the moving part may be a moving arcuate blade shroud mounted on the radially outer tip of a moving turbine blade. The static part may be a static casing positioned radially outwardly of the moving blade shroud. Alternatively, the moving part may be a rotor shaft and the static part may be a static diaphragm ring positioned radially outwardly of the rotor shaft. The labyrinth seal may thus be arranged to seal between an inner diameter of the static diaphragm ring and the radially inner rotor.
- An axial flow turbine, such as a gas turbine or steam turbine, generally includes a plurality of turbine stages, each stage comprising an annular array of angularly spaced-apart moving blades, preceded by an annular array of angularly spaced-apart static vanes whose function is to guide the turbine working fluid onto the moving blades.
- Referring to
FIG. 1 , there is shown the radially outer part of a moving blade comprising anaerofoil portion 10 and anarcuate blade shroud 11, which is mounted on and integral with the radially outer tip of theaerofoil portion 10. Adjacent blade shrouds 11 cooperate to form an annular shroud ring. A circumferentially extendingstatic casing 12 is positioned radially outwardly of, and surrounds, the moving blades. - In the particular embodiment of
FIG. 1 , eachblade shroud 11 has a radially outercastellated surface 14 formed by a plurality of axially spaced-apart, radially outer, circumferentially extendinglands 16, eachland 16 being followed by a relatively recessed, radiallyinner surface portion 18 that is circumferentially co-extensive with the land. AlthoughFIG. 1 shows a shroud surface with twolands 16, it is at the option of the skilled person to incorporate as many lands as may be convenient and useful in the particular circumstances of the turbine design being considered. Normally, however, there will be a plurality oflands 16 in order to decrease leakage of working fluid through the gap between theshroud 11 and thestatic casing 12, as hereafter explained. - Working fluid is expanded through the axial flow turbine and moves along a fluid flow path between the moving
blade aerofoils 10 in a downstream direction, as shown byarrow 19 inFIG. 1 . Alabyrinth seal 20 seals between the moving blade shrouds 11 and the radially adjacentstatic casing 12 to minimizefluid leakage 21 past the blade shrouds 11 at the tips of the moving blades. - In the particular embodiment of
FIG. 1 , thelabyrinth seal 20 includes a plurality of first circumferentially extending and axially spaced sealingfins 24 which project radially inwardly from thestatic casing 12 across the leakage fluid flow path towards thelands 16 on thecastellated surface 14 of the moving blade shrouds 11. Thelabyrinth seal 20 also includes a plurality of second circumferentially extending and axially spaced sealingfins 26 which likewise project radially inwardly from thestatic casing 12 across the leakage fluid flow path towards the relatively recessed radiallyinner portions 18 of thecastellated surface 14 of the moving blade shrouds 11. - The first and second circumferentially extending sealing
fins static casing 12 in the axial direction, such that each of thefirst sealing fins 24 is followed by asecond sealing fin 26. The first and second circumferentially extending sealingfins static casing 12. Alternatively, it may be possible to produce the fins integrally with the casing by a machining or casting process. - The distal ends or tips of each of the first and
second sealing fins castellated surface 14 of the moving blade shrouds 11, that is, during normal operation of the turbine, there are small radial clearances between the distal ends of the fins and thecastellated surface 14. Such radial clearances may be of the order of one or two millimeters and are intended to prevent or ameliorate rubbing contact between the tips of the sealingfins static casing 12 during operation of the turbine. Such rubbing contact would cause the tips of the sealingfins labyrinth seal 20. The correct radial clearances to use can be calculated by computer modeling of the operating behavior of the turbine or determined by rig tests. - Although the radial clearances chosen are generally sufficient to prevent rubbing contact between the tips of the first and
second sealing fins castellated surface 14 of the adjacent moving blade shrouds 11 during most radial excursions of the moving blade shrouds 11 relative to thestatic casing 12, larger radial excursions, which may be outside normal turbine operating behavior, can be tolerated by providingabradable material 27 on thecastellated surface 14 of the blade shrouds 11 adjacent the tips of the first andsecond sealing fins abradable material 27, which is softer than the material at the tips of the sealingfins fins fins second sealing fins fins - Abradable materials suitable for the above purpose are, for example, thermal-sprayed coatings of various types, such as cermets. A well-known alternative is Feltmetal®, comprising metal fiber felts made from a variety of high temperature resistant alloys, the fibers in the felts being randomly interlocked by a sintering process. Feltmetal® is manufactured by Technetics, 1700 E. Int'l Speedway Blvd., DeLand, Fla. 32724 USA.
- Each of the
first sealing fins 24 is inclined in an upstream direction and defines an acute angle ‘A’ relative to the radial direction. In the present case angle A is about 45 degrees away from the radial direction, but in other embodiments angle A may vary between about 10 and 70 degrees. Accordingly, each of thefirst sealing fins 24 has a linear (i.e. non-curved) upstream-facingsurface 28 which is oriented at the acute angle A, in the aforesaid range. Each of thefirst sealing fins 24 is mounted on thestatic casing 12 and projects across the leakage flow path so that its distal end is in sealing proximity with a correspondingcircumferential land 16 of thecastellated surface 14 of the moving blade shrouds 11. The inclined linear upstream-facingsurface 28 of each of thefirst sealing fins 24 cooperates with the corresponding circumferentially extendingland 16 and forms a vortex-producing flow recirculation surface operative to deflectleakage flow 21 back in an upstream direction, thereby creating recirculating vortices 25 in the leakage flow.Leakage flow 21 past the tips of thefirst sealing fins 24 is thus reduced. - Referring also to
FIG. 2 , each of thesecond sealing fins 26 includes an upstream-facingsurface 30, comprising afirst fin portion 32 which projects in a substantially radially inward direction from thestatic casing 12 across the leakage flow path, and a second,distal portion 34 adjacent to and including the fin's tip, this distal portion being inclined towards the upstream direction, i.e., towards the downstream surface of an immediately upstream sealing fin, where such a fin is present. In the embodiment illustrated inFIGS. 1 and 2 , the inclineddistal portion 34 of eachsecond fin 26 is a concavely curved portion of the upstream-facingsurface 30. This concavely curved portion forms a vortex-producing flow recirculation surface, which extends over a distance comprising about 30% of the total length L of thefin 26 measured between its tip and the surface from which it projects. In other embodiments the curvature may extend over a distance in the range of about 20% to about 50% of the fin's length between its tip and thestatic casing surface 12 from which it projects. - As an example, consider a fin with a length L of 10 mm between its point of attachment to the
surface 12 and its tip. If the curve in the distal portion of the upstream-facingsurface 30 of the fin has a radius R of 4 mm, the curve will occupy about the last 3 mm of the fin adjacent the tip, measured in the radial direction. - Whereas the concavely curved
distal portion 34 of upstream-facingsurface 30 offins 26 is shown as an arc of a circle, the skilled person will realize that the curve could alternatively be an arc of an ellipse or other conic section. - The concavely curved
distal portion 34 of upstream-facingsurface 30 offins 26 may be approximated by a straight (linear) distal portion, inclined at an angle relative to the radial direction. This is illustrated inFIG. 3 , where afin 26A of length L has an upstream-facingsurface 30A with a straightdistal portion 34A that is inclined at an angle ‘B’ to the radial direction to form a vortex-producing flow recirculation surface. Similarly to the curveddistal portion 34 inFIG. 2 ,distal portion 34A inFIG. 3 is inclined over a distance comprising about 30% of the total length L of thefin 26 measured between its tip and the surface from which it projects, but in other embodiments the inclined portion may extend over a distance comprising between about 20% and about 50% of the fin's length between its tip and the surface from which it projects. - As an example, angle B in
FIG. 3 may be in the range of about 10 degrees to about 60 degrees, preferably about 25 degrees to about 45 degrees, and if the length L of the fin is 10 mm, the inclineddistal portion 34A of the upstream-facingsurface 30A may occupy about the last 3 to 4 mm of the fin adjacent the tip, measured in the radial direction -
FIG. 4 illustrates a further alternative embodiment, which may be preferred from the aspect of enabling greater sealing efficiency. In this embodiment, the whole of the upstream-facingsurface 30B of thefin 26B is curved in the upstream direction, not merely the distal portion. In the particular case shown, the angle that the upstream-facingsurface 30B makes to the radial direction gradually increases from zero at a point where the fin projects from the static or moving surface, to a maximum angle B at thetip 340B of the fin. For example, thesurface 300B could be elliptically, parabolically or hyperbolically curved. Again, angle B may be in the range of about 10 degrees to about 60 degrees, preferably about 25 degrees to about 45 degrees. - Returning to a consideration of
FIGS. 1 and 2 , the shapes of thefins leakage fluid 21 back in an upstream direction, thus creating recirculating vortex flows 25, 36 in the axially and circumferentially extendingchambers - As the number of first and second circumferentially extending sealing
fins fins FIG. 2 has been found to provide a reduction in leakage flow between thecastellated surface 14 of the moving blade shrouds 11 and thestatic casing 12 of about 19% compared to conventional labyrinth seal designs such as that shown inFIG. 1 of EP 1001139 A1. The efficiency of an axial flow turbine including the labyrinth seal is thus appreciably improved. - It should be noted that the
shroud surface 14 is provided withalternate lands 16 and recessedportions 18 so that theleakage flow 21 has a less direct route through the labyrinth seal than would be the case if the shroud surface were merely planar. This increases the resistance of the labyrinth seal to the leakage flow. Moreover, the recessedportions 18 providevortices 36 with a greater radial height and chamber volume in which to fully develop, thereby further increasing resistance of the labyrinth seal to the leakage flow. - Although various embodiments have been described in the preceding paragraphs, it should be understood that various modifications may be made to those embodiments without departing from the scope of the following claims.
- For example, the first and/or second circumferentially extending sealing
fins static casing 12 would be castellated so that the first and second circumferentially extending sealingfins castellated surface 14 of thestatic casing 12. - Although
FIG. 1 shows four sealing fins arranged in flow series, i.e., twofirst fins 24, each of which is followed by asecond fin 26, it should be realized that if desired, this sequence could be extended indefinitely, e.g., six sealing fins comprising threefirst fins 24, each of which is followed by asecond fin 26. Conversely, in some situations, it may be possible to achieve acceptable sealing performance using twofirst fins 24, with onesecond fin 26 located between the twofins 24, or even only onefirst fin 24 followed by only onesecond fin 26. - Whereas
FIG. 1 illustrates a presently preferred arrangement, in which the most upstream fin is afirst fin 24 whose distal end is in sealing proximity to aland 16, and the immediately succeeding fin is asecond fin 26 whose distal end is in sealing proximity to a recessedsurface portion 18, it may also be possible to obtain a desirable increase in efficiency if the order of the first and second fins is reversed, so that the most upstream fin is asecond fin 26 whose distal end is in sealing proximity to a recessedsurface portion 18 and the immediately succeeding fin is afirst fin 24 whose distal end is in sealing proximity to aland 16. - A second major embodiment will now be described with reference to
FIGS. 5 to 8 . -
FIG. 5 again shows the radially outer part of a moving blade comprising anaerofoil portion 100 and anarcuate blade shroud 110, which is mounted on and integral with the radially outer tip of theaerofoil portion 100. Adjacent blade shrouds 110 cooperate to form an annular shroud ring. A circumferentially extendingstatic casing 120 is positioned radially outwardly of, and surrounds, the moving blades. - Working fluid is expanded through the axial flow turbine and moves along a fluid flow path between the moving
blade airfoils 100 in a downstream direction, as shown byarrow 190 inFIG. 1 . Alabyrinth seal 200 seals between the movingblade shrouds 110 and the radially adjacentstatic casing 120 to minimizefluid leakage 210 past the blade shrouds 110 at the tips of the moving blades. - In the particular embodiment of
FIG. 5 , thelabyrinth seal 200 includes a plurality of first circumferentially extending and axially spaced sealingfins 240 which extend radially inwardly from thesurface 122 of thestatic casing 120 across the leakage fluid flow path towards thesurface 140 of the moving blade shrouds 110. Thelabyrinth seal 200 also includes a plurality of second circumferentially extending and axially spaced sealingfins 260 which project radially outwards from thesurface 140 of the movingblade shrouds 110 across the leakage fluid flow path towards thesurface 122 of thestatic casing 120. Hence, thefirst sealing fins 240, projecting inwardly from thestatic casing 120, may be termed static sealing fins, and thesecond sealing fins 260, projecting outwardly from the movingblade shrouds 110 may be termed moving sealing fins. - The static and moving sealing
fins labyrinth seal 200, such that eachstatic sealing fin 240 is followed by a movingsealing fin 260. Thus, thestatic sealing fins 240 project into axial spaces between the moving sealingfins 260, whilst the moving sealingfins 260 project into axial spaces between the static sealing fins. The static and moving sealingfins static casing 120 and the movingblade shrouds 110, respectively. Alternatively, it may be possible to produce the fins integrally with theshrouds 110 and/or thecasing 120 by a machining or casting process. - The distal ends or tips of the
static sealing fins 240 are in sealing proximity to the movingblade shrouds 110, whilst the distal ends or tips of the moving sealingfins 260 are in sealing proximity to thestatic casing 120. This means that during normal operation of the turbine, there are small radial clearances between the distal ends of thestatic fins 240 and the movingblade shrouds 110, and between the distal ends of the movingfins 260 and thestatic casing 120. Such radial clearances are intended to prevent or ameliorate rubbing contact between the distal ends of the sealingfins blade shrouds 110 orstatic casing 120, caused by radial excursions of the movingblade shrouds 110 relative to thestatic casing 120 during operation of the turbine. Such rubbing contact would cause the tips of the sealingfins labyrinth seal 200. The correct radial clearances to use can be calculated by computer modeling of the operating behavior of the turbine, and/or determined by rig tests. - Although the radial clearances chosen are generally sufficient to prevent rubbing contact between the tips of the static and moving sealing
fins blade shrouds 110 orstatic casing 120 during most radial excursions of the movingblade shrouds 110 relative to thestatic casing 120, larger radial excursions, which may be outside normal turbine operating behavior, can be tolerated by providingabradable material 270 on or in thesurfaces blade shrouds 110 and thestatic casing 120 adjacent the tips of thestatic sealing fins 240 and the moving sealingfins 260. Theabradable material 270, which is softer than the material at the tips of the sealingfins fins labyrinth seal 200. - Abradable materials suitable for the above purpose are, for example, thermal-sprayed coatings of various types, such as cermets. A well-known alternative is Feltmetal®, comprising metal fibre felts made from a variety of high temperature resistant alloys, the fibres in the felts being randomly interlocked by a sintering process. Feltmetal® is manufactured by Technetics, 1700 E. Int'l Speedway Blvd., DeLand, Fla. 32724 USA.
- As shown more clearly in
FIG. 6 for a single one of thestatic sealing fins 240, each of the static and moving sealingfins labyrinth seal 200. In the illustrated embodiment, each sealingfin surface 300 that includes astraight fin portion 320 projecting in a substantially radial direction from either thestatic casing 120 or the movingblade shroud 110 across the leakage flow path, and adistal portion 340 near its distal end, which is inclined towards the upstream direction of the leakage flow. In the particular variant shown, the inclineddistal portion 340 is a concavely curved portion of the fin's upstream-facingsurface 240, and comprises a vortex-producing flow recirculation surface, which extends over a distance comprising about 30% of the total length L of the fins measured between their tips and the surface from which they project. In other embodiments the concave curvature may extend over a distance in the range of about 20% to about 50% of the fin's length between its tip and the static or moving surface from which it projects. - As an example, take a fin with a length L of 10 mm between its point of attachment to the surface and its tip. If the curve in the distal portion of the upstream-facing
surface 300 of the fin has a radius R of 4 mm, the curve will occupy about the last 3 mm of the fin adjacent the tip, measured in the radial direction. - Whereas in
FIGS. 5 and 6 the concavely curveddistal portion 340 of upstream-facingsurface 300 offins - The concavely curved
distal portion 340 of upstream-facingsurface 300 may be approximated by a straight distal portion, inclined at an angle relative to the radial direction. This is illustrated inFIG. 7 , where afin 260A of length L has an upstream-facingsurface 300A that includes astraight fin portion 320A projecting in a substantially radial direction from either thestatic casing 120 or the movingblade shroud 110 across the leakage flow path, and a straightdistal portion 340A that is inclined at an angle ‘B’ to the radial direction to form a vortex-producing flow recirculation surface. Similarly to the concavely curveddistal portion 340 inFIG. 2 , angleddistal portion 340A inFIG. 7 is inclined over a distance comprising about 30% of the total length L of the fin measured between its tip and the surface from which it projects, but in other embodiments the inclined portion may extend over a distance comprising between about 20% and about 50% of the fin's length between its tip and the surface from which it projects. - As an example, angle B in
FIG. 7 may be in the range of about 10 degrees to about 60 degrees, preferably about 25 degrees to about 45 degrees, and if the length L of the fin is 10 mm, the inclineddistal portion 340A of the upstream-facingsurface 300A may occupy about the last 3 to 4 mm of the fin adjacent the tip, measured in the radial direction. -
FIG. 8 illustrates a further alternative embodiment, which may be preferred from the aspect of enabling greater sealing efficiency. In this embodiment, the whole of the upstream-facingsurface 300B of the fin is concavely curved, not merely the distal portion. In the particular case shown, the angle that the upstream-facingsurface 300B makes to the radial direction gradually increases from zero at apoint 320B where the fin projects from the static or moving surface, to a maximum angle B at thetip 340B of the fin. For example, thesurface 300B could be elliptically, parabolically or hyperbolically curved. Again, angle B may be in the range of about 10 degrees to about 60 degrees, preferably about 25 degrees to about 45 degrees. - Returning to a consideration of
FIG. 5 , it should be noted that the complementary shapes of the vortex-producing flow recirculation surfaces 340 of the static and movingfins recirculating vortices 360 in the axially and circumferentially extendingchambers 400 defined between successive static and movingfins additional vortex 370 will be generated in the leakage flow before it enters the labyrinth by the flow recirculation surface of the mostupstream fin 240, though this vortex may be weaker than the vortices produced inchambers 400. Although all thevortices adjacent chambers 400 may rotate in opposed directions, thereby further increasing the resistance of thelabyrinth seal 200 to leakage flow. - As the number of static and moving sealing
fins fins FIG. 5 has been found to provide a reduction in leakage flow between the movingblade shrouds 110 and thestatic casing 120 of about 30% compared to conventional labyrinth seal designs such as that shown inFIG. 1 of EP 1001139 A1. The efficiency of an axial flow turbine including the labyrinth seal is thus appreciably improved. - Although the labyrinth seal illustrated in
FIG. 5 includes a plurality ofstatic sealing fins 240 and a plurality of moving sealingfins 260, it is possible that a labyrinth seal of this type could comprise only a single pair of fins, comprising a static sealing fin and a moving sealing fin. - Whereas
FIG. 5 illustrates a presently preferred arrangement, in which each of thestatic fins 240 precedes in flow sequence a movingfin 260, it may also be possible to obtain a desirable increase in efficiency if the order of the static and moving fins is reversed, so that moving fins precede static fins. InFIG. 5 , this would give an arrangement in which the first, third and fifth fins in streamwise sequence would be movingfins 240 and the second and fourth fins would bestatic fins 240. - Although the description above has focused on embodiments as applied to seals operating to control leakage between a static casing and moving blade shrouds, the skilled person will realize that embodiments falling within the scope of the appended claims could be applied to sealing between other types of moving and static parts, e.g., the moving part could be a turbine rotor shaft and the static part could be a static turbine diaphragm ring penetrated by the shaft.
Claims (24)
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GB1111287.7A GB2492546A (en) | 2011-07-04 | 2011-07-04 | A labyrinth seal for an axial fluid flow turbomachine |
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Also Published As
Publication number | Publication date |
---|---|
DE102012013160A1 (en) | 2013-01-10 |
GB201111287D0 (en) | 2011-08-17 |
US9057279B2 (en) | 2015-06-16 |
JP2013019537A (en) | 2013-01-31 |
GB2492546A (en) | 2013-01-09 |
JP5693529B2 (en) | 2015-04-01 |
CN102865108B (en) | 2016-05-04 |
CN102865108A (en) | 2013-01-09 |
DE102012013160B4 (en) | 2022-07-28 |
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